Don't resize the terminal buffer until dragging is released

Add a setting to enable this behavior.

Maybe the user might not want to reflow the buffer in real-time as they resize the window. Maybe they only want to have the resize occur when they finish resizing.

I'd love to see an E2E spec of this scenario before code starts getting written, because I feel it might be a little wonky in certain scenarios. Questions that would be good to be answered:

• How will we communicate the start of a move/size loop from WindowsTerminal down to the TerminalApp?
• How will this play with panes that aren't terminals?
• how do we handle maximize/restore?
• Should we pause rendering while this is happening? How should this look to the user?

From discussion in #1465